Conventionally, a dressed carcass of one head of cattle has been divided into twenty-six portions, such as loin, short plate, fillet, and the like, and these twenty-six portion-cut meats have been vacuum packaged, cooled after a film having been shrunk by heating or without the film being shrunk, and then stored and delivered at around 0 deg C. to be supplied as so-called chilled beef.
In order to further divide these portion-cut meats and supply them to end consumers, skilled technicians have been required. Recently, supermarkets and the like have had a demand for portion-cut meats, such as beef, pork, large-size fishes, chicken, and the like, which have been divided into smaller parts such that even unskilled people can process them.
In patent literature 1, the present inventor et al. disclosed a method, wherein a rolled lower film, which has gas-barrier properties and thermal fusion bonding properties, is unrolled; at least two portion-cut meats are loaded on the lower film with a spacing being given between portion-cut meats and a front end of the lower film having been fusion bonded to a front end of an upper film; rolled upper film is unrolled to cover the portion-cut meats on the lower film, and the upper and lower films are fusion bonded to each other; at a middle of a fusion bonded area, the films are cut to obtain a tubular sealed object holding portion-cut meats between the upper and lower films; this tubular sealed object is evacuated from both openings thereof; the openings are sealed for vacuum sealing to obtain a vacuum four-side sealed object containing at least two portion-cut meats; then, in a flat part between portion-cut meats contained in this vacuum packaged object, at least two seal lines are produced by using an impulse sealer, with which timings for starting heating of upper and lower heater wires differ by 0.3 to 4 sec, and then between the seal lines the films are secondary-cut.
As films for packaging of these portion-cut meats, various films, such as those as disclosed in patent literature 2 and patent literature 3, are available.
In recent years, an increasing number of mass merchandisers who want to simplify their tray packaging work, and consumers have requested that, for beef, for example, one head of cattle be divided into seventy-four portions or one hundred-eighty portions, and these be delivered, being individually vacuum packaged as separate products.
Patent literature 1: Japanese Laid-Open Publication No. 2004-161291
Patent literature 2: Japanese Laid-Open Publication No. 10-34800/1998
Patent literature 3: Japanese Laid-Open Publication No. 11-207886/1999
As a result of performing the art of the patent literature 1, for example, when smaller portion-cut meats of a pig were vacuum unitary packaged using upper and lower films having a width of 850 mm, a dividing step by using the impulse sealer took approximately 7 sec on average. Because placing a plurality of portion-cut meats in one packaging container for vacuum packaging them has been improved for a higher speed, a dividing time period of approximately 7 sec is becoming an obstacle in improvement of work efficiency. A cause for the dividing time period having been as long as approximately 7 sec was that, unless a cooling time, even if momentary, were provided after energizing and heating one of the upper and lower heater wires and before energizing the other, it would be difficult to reliably fusion bond the films, one of which has a thickness two or three times larger or smaller than that of the other.
If a period of time for energization of the upper and lower heater wires is shortened, there arises a problem in that a seal strength of a sealed part is reduced, and thus vacuum leakage may occur at a stage of distribution. On the other hand, if a sufficient period of time for cooling is not provided, there occurs a problem in that a seal line area is stretched during cutting and a vacuum leak may be produced at a seal line, resulting in damage being caused to form as a commercial product.
In addition, because of a demand for cost reduction, there is a trend for thinner films being used. With thin films, tolerances for the period of time for energization and a difference in timing for starting energization of the upper and lower heaters have been narrowed in order to provide reliable sealing by the impulse sealer while eliminating a possibility of seal breakage, and it is becoming difficult to adjust a timing of activating functions of the impulse sealer.